soft, semiorganic artificial neurons.
“The overarching goal of our
research is to try to develop devices
that can mimic the functioning of
building blocks in our body,” says
study co-author Simone Fabiano, an
organic nanoelectronics researcher
at Linköping University in Sweden.
The Venus flytrap provides an
efficient testing ground for an
interface between living creatures
and electronics that, Fabiano and his
team hope, may one day lead to fully
integrated biosensors for monitoring
human health—or a better interface
for people to control advanced
prostheses with their nerves. The
results were published in Nature
Communications in February.
This is not the first time scientists
have controlled a Venus flytrap.
Alexander Volkov of Oakwood
University has been researching
plant electrophysiology—and specifi-
cally Venus flytraps—for decades. In
2007 he and his lab hooked up silver
wires to a flytrap’s snapping mecha-
nism and ran an electric current
through the system, causing the
lobes to clamp shut.
Such experiments work because
the motion is controlled by an
apparatus similar to an animal’s
nervous system. In the flytrap, the
phloem—the tissue that transports
nutrients through a plant—contains
ion channels through which charged
particles can flow. This triggers the
plant’s lobes to close, similar to the
way electrical charge flows along an
animal’s nerves to send commands
to its muscles. But there are some
key differences between the two
systems. “In Venus flytraps, calcium
mitigates the [electrical] response,
whereas in animals, it’s usually
sodium,” says Swetha Murthy, a
biochemist at Oregon Health &
Science University, who also works
with Venus flytraps but was not
involved in the new study. Additional-
ly, the plant’s membranes are hyper-
polarized, compared with animal
neurons. This means scientists have
to use extra current to induce a
reaction in the Venus flytrap. They do
so by incorporating charged chloride
ions into their electronic device.
Despite these differences, a Venus
flytrap’s ion channel serves as a good
model for testing nerve activity,
thanks to the channel’s size. “It’s easy
to measure in experiments,” Volkov
says. And the trap’s big, clam-
shell-like closing motion is an
obvious sign that the signal hasgotten through. Plus, there are fewer
ethical considerations when it comes
to using plants, as opposed to
animals, in the lab.
To make their flytrap close, Fabiano
and his colleagues constructed a
neuronlike electronic device. They
began by screen printing carbon and
silver chloride electrodes onto a
polyester base. “It’s what you use for
printing labels on T-shirts,” Fabiano
explains. “It’s a very, very simple way
of making electronics.” Next they
attached the electrodes to the lobes
and midrib (or crease) of the plant’s
trap and ran a current through the
system—first at a high frequency and
then at a lower one. They found the
high frequency triggered a quick
response, but the low frequency was
not enough to close the trap.
This setup was somewhat similar to
Volkov’s original work and previous
research involving artificial neurons
but differed in a couple of crucial
ways. For one thing, it did not use
silicon, a rigid and relatively expensive
component of most other artificial
neurons. And unlike earlier Venus
flytrap studies, it mimicked the
structure of an actual neuron by
including a tiny gap across which
ions can jump (known as a synapsein a real nerve cell) within the
screen-printed electrodes.
Although he sees his team’s results
as encouraging, Fabiano acknowl-
edges that the system is not yet
ready to interface with human cells.
“We still have a couple of orders of
magnitude before we get to the
energy efficiency of our biological
neurons,” he says. Once the artificial
neuron becomes more efficient, he
thinks this technology could poten-
tially be used to establish a link
between a person’s signaling nerves
and an artificial limb, allowing for
seamless prosthetic control.
Volkov is not convinced the new
research represents a true break-
through. Many researchers have
designed systems to interface with
plants, he says. “Some people have
closed Venus flytraps by smart-
phone,” Volkov adds. Given the
difference in plant and animal
physiology, he is uncertain the system
could translate to real neurons
controlling an external device.
Murthy is more optimistic. “I think
this study provides strong potential to
develop and integrate implantable
devices as biosensors,” she says. “It’s
a proof-of-principle experiment.”
—Joanna ThompsonN EWS